1. Field of the Invention
The present invention relates to a convergence correction apparatus for a projection television and a method thereof, and in particular to an improved convergence correction apparatus for a projection television and a method thereof which are capable of moving convergence correction data corresponding to modes to a memory during mode switching without increasing the capacity of the memory in a projection television, so that it is possible to fabricate a more compact system, thus reducing the fabrication cost.
2. Description of the Conventional Art
In the projection television using a red, green, blue CRT, a correction data with respect to the entire portion of a screen is stored in a memory so as to correct a misconvergence phenomenon due to different light incident angles. The thusly stored correction data is read in synchronization with a raster scanning, and then is changed into an analog signal for correcting the misconvergence.
With the above-described method, it was known to increase the reliability of the picture and reduce an adjusting time. However, this method has disadvantages in that the price is higher than the conventional analog dependent convergence method which uses a passive device such as a resistor, coil, and a condenser, and when the deflection is changed, the convergence must be re-corrected.
For example, it is possible to provide various picture size modes which are obtained by adjusting the aspect ratio of a picture such as a vistar, cinema, panavision, ultra scan, etc. so that a user can enjoy more dynamic pictures as shown in FIG. 1A. Here, only the zoom modes as shown in FIGS. 1B and 1C are illustrated as examples.
FIG. 1D is a diagram illustrating an inclination of a deflection current. Namely, the deflection level is increased in accordance with the inclination of the deflection current, and thus the picture size is increased, so that the data to be corrected is increased. The correction amount of the convergence is increased from the center portion toward the edge portions thereof. In addition, the convergence must be corrected based on the changing picture size.
FIG. 2 is a block diagram illustrating a conventional digital convergence correction apparatus.
As shown therein, the conventional digital convergence correction apparatus includes a PLL unit 201 for generating a clock in synchronization with raster scan synchronous signals HBLK and VBLK inputted, an address generator 202 for receiving the clock from the PLL unit 201 and for outputting an address signal "addr", an adjusting pattern and adjusting point indication generator 203 for outputting an adjusting pattern and adjusting point indication in accordance with the address signal from the address generator 202, a memory 204 for outputting a correction data corresponding to the address signal from the address generator 202, a digital/analog (D/A) converter 205 for converting the correction data from the memory 204 into an analog signal, a low-pass filter 206 for filtering the analog signal from the D/A converter 205, an amplifier 207 for amplifying the analog signal filtered by the low-pass filter 206 and for supplying a high current to a yoke CY, an EEPROM (Electrically Erasable and Programmable Read Only Memory) 208 for storing the adjusting point data of a picture, and a microcomputer 209 for reading the adjusting point data stored in the EEPROM 208, computing the convergence, and storing the computed result into the memory 204.
The operation of the conventional digital convergence correction apparatus will now be explained with reference to the accompanying drawings. The address generator 202 outputs the address signal "addr" to the memory 204 in accordance with the clock outputted from the PLL unit 201. The memory 204 stores the data computed by the microcomputer 209 and outputs the data corresponding to the address signal "addr" from the address generator 202 to the D/A converter 205. The D/A converter 205 converts the inputted data into an analog signal, and the thusly converted analog signal is amplified by the amplifier 207, and the thusly amplified signal is transmitted to the convergence yoke CY.
Therefore, the high current is applied to the convergence yoke CY, and the magnetic field is changed, for thus correcting the misconvergence.
Conventionally, since the EEPROM 208 stores only adjusting data of the picture, the memory 204 stores a convergence correction data with respect to the entire portion of the picture by using only a few Kbit, and the memory 204 has much capacity.
FIG. 3 is a block diagram illustrating a conventional convergence correction apparatus adapted to a projection television.
As shown therein, the correction data based on a mode is stored in the memory 303 and the EEPROM 307. Namely, the microcomputer 308 computes the correction data with respect to a corresponding mode when the power is on, and inputs the memory address of the corresponding mode. Namely, a user can enjoy the picture after the correction data is inputted. The microcomputer 308 judges the output signal from the picture mode judging unit 309, and outputs an address conversion signal AC to the address generator 301, and the address of the corresponding mode is supplied to the memory 303.
Therefore, the correction data corresponding to the picture mode is converted into a correction waveform of analog through the D/A converter 305 and the low-pass filter 306. During fabrication, the correction is performed with respect to a corresponding mode, so that the adjusting point data is stored in the address corresponding to the EEPROM 307.
However, when the microcomputer 308 outputs the correction data to the memory 303, the switches 302 and 304 are switched to fixed terminals y and y'. Therefore, since the correction data from the memory 303 is not outputted to the D/A converter 305, there are displayed abnormal pictures in the intervals "a" and "c" as shown in FIG. 4.
In addition, in the conventional convergence correction apparatus, since there must be additionally provided memories based on the mode of the picture, if the number of modes is increased, a larger capacity of memory is needed, for thus increasing the fabrication cost. In addition, it is impossible to enjoy the pictures until the correction data with respect to a corresponding mode is computed based on the adjusting point data, and is stored into the memory 303. In order to shorten this duration time, if the high speed microcomputer 308 is used, the microcomputer 308 does not work during a usual operation, thereby degrading the efficiency of the system.